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The DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material.Wed, 07 Oct 2015 04:22:27 GMT2015-10-07T04:22:27ZApplication of water jet description on the de-scaling process
http://hdl.handle.net/10084/110502
Application of water jet description on the de-scaling process
Hlaváč, Libor
The paper is dealing with application of theoretical equations derived for rock disintegration onto materials with similar behavior—thick scales on hot metal rolling slabs. Penetration of water jet through a hot, rock-like material (e.g. scale) and work of the steam bubbles emerging from the water jet on the boundary between the scale layer and the hot metal material are described by a set of appropriate equations. The model is applied on the fan jets used for de-scaling process, and it provides both the qualitative and the quantitative results. These results make possible to determine the depth of penetration of water jet into the material of the scales and calculate the sizes of pieces of the disintegrated scales. Both mechanisms of water jet acting on scales, mechanical penetration to a certain depth in the material and the formation of steam bubbles inside the material, create mechanical stresses in the material of scales, especially the tensile and the shear ones. Pieces of scales are separated due to exceeding the limits of the stress and strain in the material of scales. The presented analytical equations describing the process in a simple way yield the quick and apprehensible calculation of applicable results. It is an alternative to solution of a rather complicated set of differential equations describing the mass and heat flow. The proposed theoretical base runs with technical factors and properties that can be obtained from tables or analogies with other materials or processes. The typical water pressure range of rolling mills is 16–24 MPa, the equivalent diameter of the applied water nozzle is 2 mm, the average traverse speed of the rolling slab is set to 1 m s−1, and the mean stand-off distance of the nozzle from the steel slab surface is 150 mm. Calculated depth of penetration into scales is ranging from 5 to 18 mm for these parameters, while the real thickness of scales lies between 1 and 7 mm. Simultaneously, the calculated length of the peeled layer in the direction of the jet movement ranges from 30 to 70 mm and the cutting width determined from the jet shape and the stand-off distance is 80–120 mm. Therefore, the calculated size of the scale debris is 30 × 80 mm for layers thicker than 5 mm and 70 × 120 mm for the ones thinner than 2 mm. These theoretical values correspond with sizes of real scale debris picked at the rolling mill.
V článku uvedeno Hlaváč, Libor M.
Thu, 01 Jan 2015 00:00:00 GMThttp://hdl.handle.net/10084/1105022015-01-01T00:00:00ZIndividualization of a vectorcardiographic model by a particle swarm optimization
http://hdl.handle.net/10084/110501
Individualization of a vectorcardiographic model by a particle swarm optimization
Vožda, Michal; Jurek, František; Černý, Martin
This paper presents the application of a bio-inspired method for optimizing a lifelike vectorcardiographic (VCG) model. During the model estimation, a Particle Swarm Optimization (PSO) seeks the optimal combination of all parameters that maximize the correlation coefficient (r) and minimize the Mean Squared Error (MSE) between the synthetic and directly measured VCG leads. The proposed method was tested on 52 different VCG records annotated as a healthy control (HC) from PTB database. 156 models were individualized without any previous analysis of the waves of the original records. The PSO method automatically provides very realistic models with a correlation coefficient r > 0.995 and MSE < 0.0005 mV2 for 152 of the 156 VCG signals.
Thu, 01 Jan 2015 00:00:00 GMThttp://hdl.handle.net/10084/1105012015-01-01T00:00:00ZGround track density considerations on the resolvability of gravity field harmonics in a repeat orbit
http://hdl.handle.net/10084/110500
Ground track density considerations on the resolvability of gravity field harmonics in a repeat orbit
Klokočník, Jaroslav; Wagner, Carl A.; Kostelecký, Jan; Bezděk, Aleš
One of the limiting factors in the determination of global gravity field parameters is the spatial sampling, namely during phases when the satellite is in an orbit with few revolutions for each repeat cycle. This often happens when it is freely passing (drifting) through the atmosphere and encountering a fair number of such deficient repeat orbits. This research was triggered in 2004 by the significant but only temporary, 2–3 months long, decrease of the accuracy of monthly solutions for the gravity field variations derived from GRACE. The reason for the dip was the 61/4 resonance in the GRACE orbits in autumn 2004. At this resonance, the ground track density dramatically decreased and large (mainly longitude) gaps appeared in the data-coverage of the globe. The problem of spatial sampling has been studied repeatedly (Wagner et al., 2006; Klokočník et al., 2008; Weigelt et al., 2009) and simple rules have been derived to limit the maximum order for unconstrained solutions (inversions) for the gravity field parameters or their variations from observations of a single satellite. Here we work with the latest rule from Weigelt et al. (2013) which distinguishes the maximum attainable order according to the parity of the two parameters defining the repeat orbit or orbital resonance, β the number of nodal satellite’s revolutions in α nodal days (α, β co-prime integers, the ratio β/α irreducible). This rule, that the resolvable order (in a repeat near polar orbit) should be β for odd parity (β − α) and β/2 for even parity (β − α) orbits, arose from the discovery that the number of distinct and equally spaced equatorial crossings (ascending and descending passes) for odd parity (β − α) is 2β while for even parity orbits it is only β. We extend this insight over all achievable latitudes and assess the ground track density (or coverage) by way of the maximum distances between subsatellite points at arbitrary latitude, specifically for the nearly polar (drifting) orbits of CHAMP, GRACE, and the repeat tuned GOCE. We demonstrate clearly how latitude (and also the orbital inclination) is important and affects the choice of an order resolution limit. A new rule, compromising between β and β/2 for each specific repeat orbit, is proposed, based on the average maximum distance between subsatellite points over the achievable latitudes. Although these findings allow an initial estimate of recoverability based solely on the global spatial sampling of the ground track, a more refined analysis involving the inversion of specific observations is still outstanding.
Thu, 01 Jan 2015 00:00:00 GMThttp://hdl.handle.net/10084/1105002015-01-01T00:00:00ZCommunication efficient work distributions in stencil operation based applications
http://hdl.handle.net/10084/110499
Communication efficient work distributions in stencil operation based applications
Schneible, Joseph; Říha, Lubomír; Malik, Maria; El-Ghazawi, Tarek; Alexandru, Andrei
In recent years, the use of accelerators in conjunction with CPUs, known as heterogeneous computing, hasbrou ght about signiﬁcant performance increases for scientiﬁ c applications. One of the best examples ofthis is lattice quantum chromodynamics (Q CD), a stencil operation based simulation. These simulationshave a large memory footprint necessitating the use of many graphics processing units (GPUs) in parallel.This requires the use of a heterogeneous cluster with one or more GPUs per node. In order to obtainoptimal performance, it is necessary to determine an efﬁcient commu nication pattern bet ween G PUs onthe same node and between nodes. In this paper, we present a performance model based method for min-imizing the communication time of applications with stencil o perations, s uch a s l attice Q CD, o n hetero-geneous computing systems with a non-blocking InﬁniBand interconnection network. The proposedmethod is able to increase the performance of the most computationally intensive kernel of lattice QCDby 25% due to improved overlapping of communication and computation. We also demonstrate that theaforementioned performance model and efﬁcient communication patterns can be used to determine a costefﬁcient heterogeneous system design for stencil operation based applications.
Thu, 01 Jan 2015 00:00:00 GMThttp://hdl.handle.net/10084/1104992015-01-01T00:00:00Z